Fix SEGV in ostream_wrapper

test/ostream_wrapper_test.cpp

@@ -0,0 +1,15 @@
+#include "yaml-cpp/ostream_wrapper.h"
+
+#include "gtest/gtest.h"
+
+namespace {
+class OstreamWrapperTest : public ::testing::Test {
+ protected:
+};
+
+// Tests that the Foo::Bar() method does Abc.
+TEST_F(OstreamWrapperTest, ConstructNoWrite) {
+  YAML::ostream_wrapper wrapper;
+  EXPECT_STREQ("", wrapper.str());
+}
+}